Up to 5-6% of asthmatics experience symptoms and exacerbations despite conventional treatments and have a major impact on health care systems. There is a pressing need to understand the pathophysiology of chronic severe asthma. These patients demonstrate relative resistance to the therapeutic effects of corticosteroids (CS). There are only a small number of these patients at any one institution. At the Royal Brompton Hospital, approximately 70 severe asthmatics per year are referred to a protocol for investigation and management. This project will investigate the inflammatory and cellular responses in chronic severe asthma, determine the role of CS responsiveness (CR) of these responses, and elucidate the cellular and molecular mechanisms of impaired CR. The hypothesis is that inflammatory pathways in severe asthma are magnified by signalling pathways, particularly the mitogen-activated protein kinases (MAPK), which in turn diminishes CS actions. CS actions may be impaired at receptor binding level, nuclear translocation of the activated receptor and inhibition of histone acetylation; the underlying molecular mechanisms will be investigated. Results obtained from chronic severe asthma patients will be compared to those from mild-to-moderate asthma who are well-controlled on moderate doses of inhaled CS. Sputum and blood samples will be obtained and alveolar macrophages, epithelial cells and submucosal tissue retrieved by fiberoptic bronchoscopy. The effects of an exacerbation and of high-dose oral CS will be examined. Airway tissues and cells will be analysed regarding the type of inflammation, activation of signalling pathways, releasability of cytokines, CS receptor nuclear translocation, and expression and acetylation of histones, and the effect of CS examined. The molecular mechanisms underlying loss of CR will be examined. These studies should lead to more effective therapies for chronic severe asthma.